Process for the acoustic examination of monoliths for damage and device for implementing the process

Abstract

A method and apparatus for the acoustic examination of a monolith for damage, wherein a blow of defined force is applied by a hard striker to a monolith for its acoustic examination for damage. The sound pressure distribution over a predetermined frequency range, of the sound radiated by the struck monolith is analyzed by a frequency analyzer and the result is compared with a reference curve defined for undamaged monoliths. The device for implementing the process has a receptacle for the monolith to be examined, a striker, capacitor microphones as the sound pressure receivers and an evaluation unit with a frequency analyzer.

We claim: 
     
       1. A process for the acoustic examination for damage of monolithic carrier elements of porous ceramic material for use in manufacturing of waste gas catalysts, the process comprising the steps of: fixing a monolithic body of porous ceramic material to be examined, to a stationary plate;   applying an impact force of a predetermined magnitude to a fixed monolithic body by means of a hard striker;   performing synchronously at least two measurements of sound pressure of the noise radiated by the struck body, determining from said measurements, with a time delay after the striker has struck the fixed body, sound pressure distribution over a predetermined frequency range by means of a frequency analyzer in an evaluation unit to obtain an analysis result in which an impact noise of the striker is not taken into consideration due to said time delay; and   comparing selected individual values of sound pressure obtained in said analysis result with reference values of sound pressure defined in a sound pressure reference curve for undamaged monolithic bodies,   wherein said at least two sound pressure measurements are performed in varying spreading directions, and wherein said monolithic body is a cylindrical body, and one of the two sound pressure measurements is carried out in an axial direction of said cylindrical body and the other one in a radial direction of said cylindrical body.   
     
     
       2. Process in accordance with claim 1, wherein said time delay is in the range of 5 to 30 ms. 
     
     
       3. Process in accordance with claim 1, wherein the sound pressure distribution within the frequency range between 4 and 12 kHz is determined in said determining step. 
     
     
       4. Process in accordance with claim 1, wherein said said selected individual values are compared with reference values in said comparing step at frequencies of characteristic peaks of said curve. 
     
     
       5. Process in accordance with claim 1, wherein a number of peaks within said predetermined frequency range of a curve obtained in said analysis result are compared with a number of peaks in said reference curve in said comparing step. 
     
     
       6. Process in accordance with claim 1, wherein said striker is formed as a pendulum and each examination procedure starts from the same point of a pendulum path. 
     
     
       7. Process in accordance with claim 1, wherein the striker impacts one of end faces of said cylindrical body. 
     
     
       8. Process in accordance with claim 7, wherein the striker impacts in the center of a front face of the monolithic body. 
     
     
       9. Process in accordance with claim 1, wherein said comparing step is carried out in a computer unit. 
     
     
       10. Process in accordance with claim 9, and further comprising the step of providing an indicator unit connected with said computer unit wherein said computer unit controls said indicator unit so that said indicator unit indicates whether the noise radiated by the monolithic body being examined lies within or outside the reference curve. 
     
     
       11. A device for the acoustic examination for damage of monolithic carrier elements of porous ceramic material for use in manufacturing of waste gas catalysts, the device comprising: receptacle means for holding a a cylindrical monolithic body of porous ceramic material, being examined;   a striker assembly including a movable striker for applying an impact force of a predetermined magnitude to said monolithic body fixed in said receptacle means;   sound pressure receiver means for performing synchronously at least two sound pressure measurements in varying spreading directions, of the noise radiated by a struck monolithic body; and   an evaluation unit including a computer unit and connected to said sound pressure receiver means for determining from said measurements, with a time delay after the striker has struck the fixed monolithic body, sound pressure distribution over a predetermined frequency range to obtain an analysis result in which an impact noise of the striker is not taken into consideration due to said time delay and comparing selected individual values of sound pressure obtained in said analysis result with reference values of sound pressure defined in a sound pressure reference curve for undamaged monolithic bodies.   
     
     
       12. Device in accordance with claim 11, and further comprising an indicator unit connected to said computer unit for indicating whether the monolithic body being examined has been found by said evaluation unit to be defective. 
     
     
       13. Device in accordance with claim 11, wherein said receptacle means includes three supports for placement of the monolithic body being examined. 
     
     
       14. Device in accordance with claim 11, wherein said receptacle means includes a holding plate and at least one support in the form of a holding element adapted to a monolithic to be examined. 
     
     
       15. Device in accordance with claim 14, wherein said holding plate is attached on a baseplate by a quick-gripping device. 
     
     
       16. Device in accordance with claim 13, wherein each of said supports has at each of points of contact with the monolithic body to be examined, damping elements made of an elastically resilient material. 
     
     
       17. Device in accordance with claim 11, wherein said striker assembly further comprises a pendulum having a pendulum rod on which the striker forms a pendulum mass. 
     
     
       18. Device in accordance with claim 17, wherein said striker consists of a ferromagnetic material and the striker assembly further comprises an electromagnet arranged at an upper end point of a pendulum path of the striker. 
     
     
       19. Device in accordance with claim 11, wherein said sound pressure receiver means includes two sound pressure receivers which are arranged in such a way that one receiver is directed towards a front end face facing away from the striker assembly and the other receiver is directed towards a peripheral surface of the monolithic body to be examined. 
     
     
       20. Device in accordance with claim 19, wherein said two sound pressure receivers are capacity microphones. 
     
     
       21. Device in accordance with claim 11, wherein said evaluation unit comprises an FFT-frequency analyzer. 
     
     
       22. Device in accordance with claim 11, wherein said computer unit is constructed to provide said time delay in the range between 5 and 30 ms after the striker has struck the monolithic body. 
     
     
       23. Device in accordance with claim 12, wherein said indicator unit includes lamps.